A shout-out to “Diary of a Wimpy Kid’’ author Jeff Kinney for salvaging an unhappy birthday for a 9-year-old Oregon boy. When no one showed up to Mahlon Layne’s “Wimpy Kid’’-themed birthday party, the boy’s mom blogged about it. The heartbreaking story was widely shared and, somehow, came to the attention of Kinney, who lives in Plainville. The best-selling author made a Facetime call to Mahlon and also sent him an autographed copy of his new, not-yet-released book. “He’s beaming,’’ Mahlon’s mom, Kristen, told People.com. “He’s saying, ‘Jeff Kinney is my friend!’ He’s been guarding [the book] with his life.’’